1. Field of the Invention
This invention relates to a starter system for an internal combustion engine, for starting the engine by a hydraulic actuator driven by hydraulic pressure.
2. Description of the Prior Art
Conventionally, a starter system of this kind has been proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 2001-82202. FIG. 12 schematically shows the arrangement of the starter system. This starter system 350, which is a hydraulic motor-driven type, is comprised of an electric motor 351, an oil pump 352 driven by the electric motor 351, an accumulator 353 for storing hydraulic pressure boosted by the oil pump 352, a hydraulic motor 355 connected to the accumulator 353 via an oil passage 354, and a solenoid valve 356 arranged in the oil passage 354. A drive shaft 355a of the hydraulic motor 355 is connected to a drive shaft 359a of a timing pulley 359 via a reduction gear 357 and a one-way clutch 358. The timing pulley 359 is connected to a timing pulley 362 of an internal combustion engine (hereinafter referred to as xe2x80x9cthe enginexe2x80x9d) 361 via a synchronous timing belt 360. Further, the timing pulley 362 is mounted to one end of a crankshaft 363.
According to the above construction, when the engine 361 is started, the solenoid valve 356 opens the oil passage 354, whereby hydraulic pressure is supplied from the accumulator 353 to the hydraulic motor 355 to drive the same for rotation. Then, the rotation of the hydraulic motor 355 is transmitted to the crankshaft 363 via the reduction gear 357, the one-way clutch 358 and the synchronous timing belt 360 to thereby start the engine 361. During operation of the engine 361 after the start thereof, transmission of torque from the crankshaft 363 to the hydraulic motor 355 is inhibited by action of the one-way clutch 358.
In general, if an engine stops halfway in a compression stroke when the operation of the engine is stopped or when the start of the same has failed, the crankshaft of the engine can be urged by pressure of the compressed air to rotate reversely to a stable position. In this case, since the direction of torque is reversed from the normal direction thereof, the one-way clutch 358 of the above starter system 350 transmits reverse torque to the hydraulic motor 355. This causes the hydraulic motor 355 to rotate in the reverse direction to act as a hydraulic pump. On the other hand, the oil passage 354 is held in a closed state by the solenoid valve 356 except when the engine is started. As a result, the hydraulic fluid pressurized to a high pressure level when the operation of the engine is stopped flows into the closed portion of the oil passage 354 between the hydraulic motor 355 and the solenoid valve 356, thereby developing high impact pressure within the oil passage 354. The high impact pressure causes the drive shaft 355a of the hydraulic motor 355 to generate large impact torque which can adversely affect a torque-transmitting system including the hydraulic motor 355 and the one-way clutch 358 as well as a hydraulic circuit system including the solenoid valve 356 and the oil passage 354. Similarly, when the start of the engine has failed, although the oil passage 54 is held open by the solenoid valve 356, high impact pressure can be generated e.g. due to a pressure loss in the solenoid valve 356.
Further, another starter system of the above-mentioned kind has been proposed e.g. by Japanese Laid-Open Utility Model Publication (Kokai) No. 59-73579. This starter system includes an electric motor, and a hydraulic motor, and is capable of starting an engine by selectively using the two motors. The electric motor has a pinion gear splined to a rotational shaft thereof. At the start of the engine, a plunging mechanism causes the pinion gear to axially slide toward the engine, for meshing engagement with a ring gear integrally formed with a crankshaft of the engine. On the other hand, the hydraulic motor is arranged on an opposite side to the pinion gear with respect to the electric motor, and serially connected to the electric motor via a one-way clutch arranged coaxially with the rotational shaft of the hydraulic motor. The hydraulic motor is driven by hydraulic pressure accumulated within the accumulator. The operation or stoppage of the hydraulic motor is controlled according to the hydraulic pressure accumulated in the accumulator, by opening and closing of a solenoid valve arranged between the accumulator and the hydraulic motor. The pressure accumulation is carried out by utilizing regenerative energy under conditions that the hydraulic pressure within the accumulator is equal to or lower than a predetermined value and that the vehicle is decelerating.
According to this starter system, when the engine is started, the pinion of the electric motor is brought into meshing engagement with the ring gear by the plunging mechanism, and when the hydraulic pressure within the accumulator is equal to or higher than the predetermined value, the hydraulic motor is driven. As a result, torque of the hydraulic motor is transmitted to the rotational shaft of the electric motor via the one-way clutch, and then further transmitted from the pinion gear to the ring rear, whereby the engine is started. On the other hand, when the hydraulic pressure within the accumulator is lower than the predetermined value, the hydraulic motor is stopped, and the electric motor is driven to start the engine. In this case, the electric motor and the hydraulic motor are disconnected from each other by the one-way clutch, which prevents the hydraulic motor from applying rotational load to the electric motor.
Normally, the hydraulic motor and the electric motor have respective different torque characteristics. More specifically, the hydraulic motor provides larger output torque than the electric motor, and the rise of rotational speed of the hydraulic motor is more rapid than that of the electric motor. Therefore, the hydraulic motor is characterized by being capable of starting the engine quickly. The quick starting of the engine is advantageous in reducing a time period during which the pinion gear and the ring gear are engaged with each other, thereby suppressing generation of noise due to the engagement between the two gears, as well as in ensuring smooth startability when the engine is frequently stopped and started by application of xe2x80x9cidle stopxe2x80x9d e.g. in traffic congestion. The xe2x80x9cidle stopxe2x80x9d is an engine operation control technique for stopping the operation of the engine when the engine speed is low under predetermined operating conditions of the engine including a fully warmed-up condition thereof. This technique has come to be increasingly valued as measures of environmental protection and fuel economy.
However, in the above conventional starter system, since the hydraulic motor is serially connected to the rotational shaft of the electric motor, when the engine is to be started by the electric motor, transmission of torque from the electric motor to the hydraulic motor is inhibited by free or idle rotation of the one-way clutch, whereas when the engine is to be started by the hydraulic motor, the torque of the hydraulic motor is transmitted to the electric motor via the one-way clutch, whereby the electric motor is caused to rotate at the same rotational speed as the hydraulic motor. This makes a brush in constant contact with the rotational shaft of the electric motor prone to wear or abrasion. This wear of the brush is particularly conspicuous when the high torque characteristic of the hydraulic motor is utilized for restarting the engine in an idle stop mode, so as to start the engine quickly, because the starting rotational speed of the engine is higher than when the electric motor is used. As the brush wears to a larger degree, the rotational resistance due to friction is increased, whereby transmission efficiency in transmitting torque from the hydraulic motor to the engine is lowered. This adversely affects the startability of the engine, and makes it necessary to design a hydraulic motor such that it has an larger output.
Further, as the hydraulic motor increases the starting rotational speed, the electric motor is required to be designed to have a robuster structure so as to endure high rotational speeds, though it is not originally necessary for engine starting operation, resulting in an extra increase in costs. Moreover, when the electric motor is disabled by fixture of movable components caused by entry of a foreign matter, it is also impossible to start the engine by using the hydraulic motor, so that the starting of the engine becomes totally impossible. In short, if quick starting by the hydraulic motor is to be executed so as to take advantage of the above characteristic of the hydraulic motor, it is required to employ an expensive electric motor capable of enduring high rotational speeds, which results in an increase in manufacturing costs. A possible solution to this problem is to provide overdrive/reduction mechanisms having respective different overdrive/reduction characteristics for the hydraulic motor and the electric motor, respectively. In this case, however, it is necessary to design another starter system anew, which also causes an increase in manufacturing costs. In addition, space for arranging the two overdrive/reduction mechanisms is needed, and hence the starter system is inevitably increased in size.
It is a first object of the invention to provide a starter system for an internal combustion engine, which is capable of preventing wear of a brush of an electric motor ascribable to the combined use of the electric motor with a hydraulic actuator and the resulting increase in the rotational resistance due to friction of the brush, as well as capable of using one of the hydraulic actuator and the electric motor without difficulty even when the other is disabled.
It is a second object of the invention to provide a starter system for an internal combustion engine, which is capable of starting the engine by selectively making use of a driving force from a hydraulic actuator or a driving force from an electric motor at a properly increased or decreased rotational speed without any interference therebetween, and which can be constructed by a compact design and at a reduced cost.
It is a third object of the invention to provide a starter system for an internal combustion engine, which is capable of preventing a hydraulic actuator, a hydraulic pressure supply control valve and an oil passage from being adversely affected by reverse torque from the engine due to stoppage of operation of the engine or failure in starting the same.
To attain the above objects, the present invention provides a starter system for an internal combustion engine, for starting the engine by driving a crankshaft for rotation,
the starter system comprising:
a hydraulic actuator that is driven by hydraulic pressure;
a first rotational shaft that is driven for rotation by the hydraulic actuator;
an electric motor;
a second rotational shaft that extends in parallel with the first rotational shaft and is driven for rotation by the electric motor;
a driven gear that rotates in unison with the crankshaft;
a driving gear that is brought into meshing engagement with the driven gear when the engine is started;
a third rotational shaft that is connected to the driving gear;
a first driving force-transmitting mechanism that connects the first rotational shaft and the third rotational shaft to each other in a disconnectable manner, for transmitting rotation of the first rotational shaft to the third rotational shaft; and
a second driving force-transmitting mechanism that connects the second rotational shaft and the third rotational shaft to each other in a disconnectable manner, for transmitting rotation of the second rotational shaft to the third rotational shaft.
According to this starter system for an internal combustion engine, the first rotational shaft that is driven for rotation by the hydraulic actuator and the second rotational shaft that is driven for rotation by the electric motor extend in parallel with each other. Further, the first driving force-transmitting mechanism disconnectably connects the first rotational shaft to the third rotational shaft having the driving gear connected thereto, while the second driving force-transmitting mechanism disconnectably connects the second rotational shaft to the third rotational shaft. In this construction, when the engine is to be started by the hydraulic actuator, the driving gear is brought into meshing engagement with the driven gear which rotates in unison with the crankshaft, and the hydraulic actuator is driven with the first driving force-transmitting mechanism being held in a connection state in which this mechanism connects the first and third rotational shafts and the second driving force-transmitting mechanism being held in a disconnection state in which this mechanism disconnects the second and third rotational shafts from each other. As a result, the rotation or torque of the hydraulic actuator is transmitted to the third rotational shaft via the first rotational shaft and the first driving force-transmitting mechanism, and then further transmitted to the driven gear via the driving gear, whereby the engine is started. In this case, since the second rotational shaft is held disconnected from the third rotational shaft by the second driving force-transmitting mechanism, no driving force is transmitted from the engine or the hydraulic actuator to the electric motor, and hence the electric motor is neither caused to rotate nor offers a rotational resistance.
As described above, the starter system of the present invention makes it possible to selectively transmit one of the driving forces of the hydraulic actuator and the electric motor to the internal combustion engine in a state of transmission of a driving force between the hydraulic actuator and the electric motor being completely inhibited, thereby starting the engine. In other words, whichever of the hydraulic actuator and the electric motor may be used to start the engine, the hydraulic actuator or the electric motor can be operated independently of each other without causing rotation of the other. As a result, it is possible to prevent wear of a brush of the electric motor due to the use of the electric motor in combination with the hydraulic actuator, and an increase in rotational resistance due to friction resulting from the wear of the brush. Further, it is not necessary to provide an extra design so as to increase the robustness of the electric motor to adapt the same to the high rotational speed characteristic of the hydraulic actuator. Moreover, even when one of the hydraulic actuator and the electric motor is disabled, it is possible to use the other to start the engine without any difficulty.
Preferably, the first and second driving force-transmitting mechanisms are formed by respective first and second one-way clutches that allow transmission of respective rotations of the first and second rotational shafts to the third rotational shaft only when the first and second rotational shafts rotate in respective directions for driving the third rotational shaft.
According to this preferred embodiment, when the engine is to be started by the hydraulic actuator, the rotation of the first rotational shaft is transmitted to the third rotational shaft via the first one-way clutch, whereas the second one-way clutch performs idle or free rotation so that the second and third rotational shafts are in a state disconnected from each other. On the other hand, when the engine is to be started by the electric motor, inversely to the above case, the rotation of the second rotational shaft is transmitted to the third rotational shaft via the second one-way clutch, whereas the first one-way clutch performs idle or free rotation so that the first and third rotational shafts are in a state disconnected from each other. Thus, by implementing the first and second driving force-transmitting mechanisms by the respective one-way clutches, it is possible to make use of one of the hydraulic actuator and the electric motor and at the same time hold the other in a disconnected state, through the simple arrangement including the clutches, to thereby start the engine, with ease and without any need to execute control operation therefor.
Preferably, the starter system includes a planetary gear set having a sun gear, a carrier, and a ring gear, the second rotational shaft being connected to one of the sun gear, the carrier, and the ring gear, and
the first rotational shaft being connected to another of the sun gear, the carrier, and the ring gear of the planetary gear set, and
the third rotational shaft being connected to a remaining one of the sun gear, the carrier, and the ring gear of the planetary gear set.
According to this preferred embodiment, the second rotational shaft driven by the electric motor, the first rotational shaft driven by the hydraulic actuator, and the third rotational shaft provided with the driving gear are connected to one, another, and the remaining one of the sun gear, the carrier, and the ring gear of the planetary gear set. Accordingly, when the engine is to be started by the hydraulic actuator, the driving gear is brought into meshing engagement with the driven gear integrally formed with the crankshaft, and at the same time, the hydraulic actuator is driven for rotation by hydraulic pressure accumulated in the accumulator. As a result, the rotation of the first rotational shaft driven by the hydraulic actuator is transmitted from the another of the sun gear, the carrier, and the ring gear to the third rotational shaft via the remaining one of these, and then further transmitted to the driven gear via the driving gear, whereby the engine is started. On the other hand, when the engine is to be started by the electric motor, the driven gear is brought into meshing engagement with the driving gear, and the electric motor is driven for rotation. The rotation of the second rotational shaft driven by the electric motor is transmitted from the one of the sun gear, the carrier, and the ring gear to the third rotational shaft via the remaining one, and further via the driving gear to the driven gear, whereby the engine is started.
As described above, according to the above preferred embodiment, it is possible to transmit the driving force of the hydraulic actuator or the electric motor to the third rotational shaft via the planetary gear set without causing interference between the hydraulic actuator and the electric motor. Further, since the driving force-transmitting mechanism for the hydraulic actuator and the electric motor is formed by a single planetary gear set, it is possible to make the starter system compact in size and manufacture the same at a reduced cost.
More preferably, the starter system further comprises first fixing means for fixing the one of the sun gear, the carrier, and the ring gear, to which the second rotational shaft that is driven by the electric motor for rotation is connected, when the engine is to be started by the hydraulic actuator, and
second fixing means for fixing the another of the sun gear, the carrier, and the ring gear, to which the first rotational shaft that is driven by the hydraulic actuator for rotation is connected, when the engine is to be started by the electric motor.
According to this preferred embodiment, when the engine is to be started by the hydraulic actuator, the driving force of the hydraulic actuator is taken out by fixing or making immovable the one of the sun gear, the carrier and the ring gear, to which the second rotational shaft that is driven by the electric motor for rotation is connected, by using the first fixing means, and delivered to the third rotational shaft at an overdrive/reduction ratio dependent on the gear ratio of the planetary gear set. Similarly, when the engine is to be started by the electric actuator, the driving force of the electric motor is taken out by fixing or making immovable the one of the sun gear, the carrier and the ring gear, to which the first rotational shaft that is driven by the hydraulic actuator for rotation is connected, by using the second fixing means, and delivered to the third rotational shaft at an overdrive/reduction ratio different from that in the case of the hydraulic actuator being used. Thus, one of the driving forces of the hydraulic actuator and the electric motor can be selectively taken out without causing any interference between the hydraulic actuator and the electric motor, as well as to obtain overdrive/reduction ratios different from each other. In short, the planetary gear set functions not only as a driving force-transmitting mechanism, but also as an overdrive/reduction mechanism for the hydraulic actuator and the electric motor. This makes it possible to manufacture the starter system further compact in size at a reduced cost.
Alternatively, if the first and second fixing means are formed by respective locking means for mechanically locking the second rotational shaft that is driven by the electric motor and the first rotational shaft that is driven by the hydraulic actuator, fixing operations by the respective fixing means can be performed by mechanically locking the respective first and second rotational shafts, so that it is possible to easily and reliably carry out switching between the output of the driving force of the hydraulic actuator and that of the driving force of the electric motor.
Further preferably, the starter system further comprises an accumulator for storing hydraulic pressure, an oil passage connected to the accumulator, and third fixing means for fixing the remaining one of the sun gear, the carrier, and the ring gear, to which the third rotational shaft that is connected to the driven gear is connected, to thereby transmit a driving force of the electric motor to the hydraulic actuator and cause the hydraulic actuator to rotate the first rotational shaft in a direction opposite to a direction in which the first rotational shaft is driven for rotation, to thereby cause the hydraulic pressure to be accumulated in the accumulator via the oil passage.
According to this preferred embodiment, hydraulic pressure is accumulated in the accumulator by fixing the remaining one of the sun gear, the carrier, and the ring gear, to which the third rotational shaft is connected, to thereby transmit the driving force of the electric motor to the hydraulic actuator and cause reverse rotation of the first rotational shaft, whereby the hydraulic pressure is accumulated in the accumulator. Thus, it is possible to utilize the hydraulic actuator to accumulate the hydraulic pressure in the accumulator, and hence a dedicated oil pump or electric motor for the pressure accumulation can be dispensed with.
Alternatively, if the above third fixing means is formed by locking means for mechanically locking the third rotational shaft, the fixing operation by the third fixing means can be performed by mechanically locking the third rotational shaft, so that the hydraulic actuator can easily and reliably perform operation for the pressure accumulation.
Preferably, the third rotational shaft is connected to the ring gear, the second rotational shaft is connected to the sun gear, and the first rotational shaft is connected to the carrier.
As described in Description of the Prior Art, when the torque characteristic of the hydraulic actuator and that of the electric motor are compared with each other, the output torque of the hydraulic actuator is larger and hence suitable for quick starting by overdrive, whereas the output torque of the electric motor is smaller, and hence it is preferably output at a reduced rotational speed. According to the above preferred embodiment, since the output shaft (third rotational shaft), the electric motor, and the hydraulic actuator are each connected to the planetary gear set as described above, the rotation of the electric motor is output at a reduced rotational speed, while that of the hydraulic actuator is output at an increased rotational speed. Therefore, the starter system can be easily selectively placed in respective operative statuses in which the rotational speed of the output shaft is increased and decreased, in a manner adapted to the respective torque characteristics of the hydraulic actuator and the electric motor.
Preferably, the starter system of the invention further comprises a hydraulic pressure supply control valve arranged in the oil passage connected to the hydraulic actuator, for controlling the hydraulic pressure to be supplied to the hydraulic actuator via the oil passage, and
a torque limiter mechanism for suppressing an increase in the hydraulic pressure when a reverse torque equal to or larger than a predetermined value and acting in a direction opposite to a direction for starting the engine acts on the hydraulic actuator during stoppage of rotation of the engine.
According to this preferred embodiment, when the engine is started, the hydraulic pressure supply control valve opens the oil passage to permit supply of hydraulic pressure to the hydraulic actuator via the oil passage, whereby the hydraulic actuator is driven for rotation. The rotation of the hydraulic actuator is transmitted to the engine, whereby the engine is started. Further, even if a reaction force from the engine generated due to stoppage of the engine or failure in starting the same causes reverse rotation of the engine, causing the hydraulic actuator to act as an oil pump to increase the hydraulic pressure, the torque limiter mechanism prevents the hydraulic pressure from being further increased when a reverse torque equal to or larger than the predetermined value acts on the hydraulic actuator.
As described above, when the engine is being stopped if the reverse torque acting on the hydraulic actuator becomes equal to or larger than the predetermined value, the torque limiter mechanism is operated to limit the hydraulic pressure, so that an excessively large torque is not generated when the engine is stopped, and further large impact torque is prevented from being generated in the hydraulic actuator. Therefore it is possible to prevent the hydraulic actuator, the hydraulic pressure supply control valve, and the oil passage from being adversely affected by large impact torque.
Further preferably, the torque limiter mechanism is a relief valve arranged in the oil passage, for opening the oil passage when the hydraulic pressure in the oil passage becomes equal to or larger than a predetermined pressure corresponding to the reverse torque equal to or larger than the predetermined value.
According to this preferred embodiment, since the relief valve is arranged in the oil passage between the hydraulic actuator and the hydraulic pressure supply control valve, it is possible to open the oil passage by the relief valve to thereby relieve the hydraulic pressure. Therefore, generation of excessive hydraulic pressure within the oil passage can be prevented.
Alternatively, the torque limiter mechanism is a clutch arranged between the engine and the hydraulic actuator, for suppressing an increase in the reverse torque transmitted from the engine to the hydraulic actuator, when the reverse torque becomes equal to or larger than the predetermined value.
According to this preferred embodiment, the clutch is arranged between the engine and the hydraulic actuator, and when the reverse torque from the engine has become equal to or larger than the predetermined value, the clutch is operated to prevent the torque transmitted from the engine to the hydraulic actuator from being increased. This prevents excessive reverse torque from acting on the first rotational shaft of the hydraulic actuator, as well as resultant generation of excessive hydraulic pressure within the oil passage.
Preferably, the starter system further comprises a discharge oil passage for discharging the hydraulic pressure from the hydraulic actuator, and the hydraulic pressure supply control valve can open or close the oil passage and the discharge oil passage simultaneously.
According to this preferred embodiment, since it is possible to simultaneously open or close the oil passage, via which hydraulic pressure is supplied, and the discharge oil passage, it is possible to reduce time wasted before re-start of rotation of the hydraulic actuator when it is driven again.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.